The invention relates to a McCulloh receiver for processing coded alarm signals on a McCulloh loop and is especially arranged for supplying these coded alarm signals to a computer for processing.
As the crime rate has historically been increasing, it has been necessary for business establishments to provide a security system to guard against the possibility of a burglary occurring during non-business hours or a hold-up occurring during business hours. Large business establishments can well afford to have their own internal security force for patrolling those establishments to uncover or prevent security problems. However, smaller business establishments cannot afford to provide their own internal security force in the form of guards for patrolling their premises; therefore, to meet their needs, central station burglar alarm operations have been established to provide a security service to these smaller concerns.
This central station typically has a plurality of alarm indicators each connected over a leased telephone line to a corresponding subscriber. A subscriber may have a single line dedicated to himself only (direct wire) or he may share a party line (McCulloh loop). The subscriber has on his premises an alarm transmitter for transmitting an alarm signal over the telephone line to the alarm indicators at the central stations.
A typical McCulloh loop comprises a line side and a ground side connected to either side of a battery such that line current normally flows in the loop. A transmitter sends its coded alarm to the central station by opening and grounding the loop.
Each subscriber on a McCulloh loop has a McCulloh transmitter for transmitting a message of a code which particularly identifies his specific premises. The coded message from a particular subscriber can identify the type of alarm, e.g. burglary, fire or the line, as well as the subscriber sending the alarm.
A more expensive form of transmitting an alarm signal to the central station is the direct wire system. In a direct wire system, a single leased line is dedicated to a single subscriber. The central station then monitors the current level on the direct wire to determine whether an alarm condition exists at the remote premises.
One of the functions of the operator at the central station is to monitor his alarm indicators to determine whether an alarm condition exists at a remote premises when an alarm signal has been received. His first function, upon receiving an alarm signal, is to see if that alarm signal represents an opening or closing of the premises according to an opening and closing schedule. If the alarm signal is received at 9 o'clock in the morning and the event schedule indicates that the owner usually opens his business establishment at 9 o'clock in the morning, the alarm signal is noted but no further action is taken. However, if the alarm signal is received at 7 o'clock in the morning, the central station then dispatches a security guard or police to that remote establishment.
Since there may be many hundred subscribers to a central station service, the number of alarms occurring during a normal opening time or closing time can be substantial so that several operators have to be employed to monitor these signals. By computerizing the central station, e.g. according to the Witt el al. application Ser. No. 390,232 filed Aug. 21, 1973, most of these operators can be eliminated and the computer can then perform the function of monitoring the alarm signals and comparing them to an event schedule to determine whether an alarm situation exists. If an alarm situation exists, the computer prints out to the operator or otherwise displays to the operator the procedure to be followed which may be to first contact the remote subscriber to determine whether the owner has violated his own event schedule, to then call the owner at home and then to contact the police or security force. Since a computer is used to process the signals received from the remote premises, the signals transmitted by the receivers in the central station to the computer must be of a form which allows the computer to process them.